The present invention relates to a motion sensing arrangement, including an active sensor element which cooperates with a pulse generator, wherein the pulse generator by its motion influences an electromagnetic field which is sensed by way of at least two field-sensitive components, the sensor element producing a binary signal which contains data about whether the field-sensitive components sense identical or different field strengths.
Arrangements of this type are generally termed as active motion sensors because the associated sensor elements require a supply voltage of their own. The term `motion` includes changes of position, displacements, numbers of rotation and motional speeds. Motion sensors are used in the field of mechanical engineering, more particularly in the automotive vehicle industry, and above all in the field of application of controlled brakes, position sensors, angular position sensors, motor-driven adjustment devices or for sensing wheel revolutions.
Motion sensors normally include a pulse generator which is mechanically connected to the part being moved, and a sensor element which scans the pulse generator in a contact-free manner. Such a scanning operation is performed by way of light, high frequency, electric or magnetic fields, in particular by permanent-magnetic fields. All these fields are referred to as electromagnetic fields.
Hole discs, toothed wheels and magnetized structures can be used as pulse generators. A defined air slot is arranged between the pulse generator and the sensor element.
Active motion sensors are operated, for example, by means of the Hall effect or the magnetoresistive effect of thin permalloy layers. The associated sensor elements are provided as chips in silicon or thin film technology. In addition to at least two magnetic-field sensitive components, comprising sensor surface zones, frequently, associated signal amplification electronics, a Schmitt trigger and a protection wiring are mounted on the chip. Embodiments with three-conductor feeds and with two-conductor feeds are known in the art. The present invention can be used for all variations of active sensors. The objective is to improve and extend the possible applications of sensors of this type. In the sensor circuitry, for example, two field-sensitive components are operated in a difference circuit, or four field-sensitive components are operated in a bridge circuit. A binary output signal is generated by an amplifier/trigger circuit in the zone of a nominal air slot irrespective of the size of the air slot. Information about the motion of the pulse generator is obtained from the edge changes of the binary output signal.
The difference circuit or bridge circuit of several field-sensitive components is used, among others, in order to minimize disturbing effects on the output signal which are due to manufacturing tolerances, interference fields and temperature effects. The analysis of a field difference instead of an absolute field strength is common to the difference and bridge circuits. The side effect of the methods is that when a supply voltage is applied, initially, the position of the pulse generator cannot be indicated.
When both field-sensitive components are in the zone of the high field strength, the difference is equal zero exactly as in a position where both field-sensitive components are in a zone of low field strength. Only after one of the sensor components has undergone a change in the field strength (and the other component is still in a zone of the original field strength), is it possible to exactly define an initial position by way of the difference of the field strengths. However, it is desired in many cases of technical applications to be provided with an information about whether the field-sensitive components are in a zone or low or high field strength immediately when the supply voltage is activated.
For example, a binary output signal does not permit an implication of the size of the air slot between the pulse generator and the sensor element. However, when a limiting air slot is exceeded, the output signal is abruptly stopped because it remains under a sensitivity threshold inside the sensor. When an active sensor is inadvertently operated to the limits of its maximum allowed air slot due to inappropriate installation, a sufficient amount of dynamic deformation of the kinematics between the sensor element and the pulse generator will possibly increase the air slot so that the limiting air slot is exceeded and the signal discontinues.
Therefore, an object of the present invention is to provide an arrangement of the above-mentioned type which permits the supply of data about the spacing between the pulse generator and the sensor element instantaneously upon activation of the supply voltage.